This invention relates to a process for removing chloroprene dimers from polychloroprene.
Polychloroprene, manufactured by emulsion polymerization, contains dimers of the monomer 2-chloro-1,3-butadiene including trans-1,2-dichloro 1,2-divinylcyclobutane, 1-chloro-5-(1-chlorovinyl)cyclohexane, 1-chloro-4-(1-chlorovinyl)cyclohexane, and 1,6-dichloro-1,5-cyclooctadiene, among other chloroprene dimers. The chloroprene dimers are formed during polymerization and they are ultimately dissolved throughout the resulting polychloroprene. Merely drying polychloroprene does not remove chloroprene dimers because these contaminants are dissolved in the polychloroprene and not in the water on the surface of the polychloroprene. Chloroprene dimers have a pungent, unpleasant odor which requires their removal for many subsequent uses. Chloroprene dimers have been removed from polychloroprene by isolating the polymer, made by an emulsion polymerization process, on freeze rolls to form a thin frozen film of polymer 500 microns thick or less. The film is washed with hot water, partially dried between two opposing squeeze rolls and the film is carried, festoon fashion, through an oven. This procedure is costly in terms of energy and manpower and is inflexible because it can only be used with polymers which can be formed into a pliable yet tough film. It has now been discovered that chloroprene dimers can be readily removed from the polychloroprene by a novel and economical process employing an extruder isolation procedure.